We presented three cases of collagen diseases complicated with myelodysplastic syndrome (MDS). To our knowledge, MDS following collagen disease is very rare, and only seven cases have been reported previously. First case (a 40-years old woman) had suffered from rheumatoid arthritis, systemic lupus erythematosus and Sjögren's syndrome for 16 years. Second case (a 65-years old woman) had suffered from rheumatoid arthritis for 15-years. Third case (a 63-years old woman) had suffered from progressive systemic sclerosis for 16 years. These patients developed MDS. After onset of MDS, cytopenia progressed rapidly within half a year. In the types of MDS, case 1 and case 2 had refractory anemia and case 3 had refractory anemia with excess of blasts and a preleukemic state. Case 2 had a clonal abnormality of haemopoietic stem cells. It is unlikely that MDS in our cases are caused by mutant agents or irradiation. These results suggest MDS may be contributed to long-term immunodysfunction found in these collagen diseases.